Auditory damage following noise over-exposure and carbon dioxide inhalation in chinchilla

Fifteen chinchilla were exposed to a 123-dB SPL narrow band noise for 50 minutes. Immediately following noise exposure they were placed in an atmosphere of either Carbogen (5% CO₂/95% O₂), Carmal (5% CO₂ /21% O₂ /74% N₂), or air for 20 minutes. Each of the three groups contained five chinchilla and the average preexposure auditory brainstem electrical response (ABER) thresholds of each group were approximately equal.

Twenty-six days following noise exposure the experimenter, without knowing which gas mixture the animals received, established ABER thresholds to tone bursts, prepared the cochleae for histologic study, and conducted hair cell counts to establish the extent of noise-induced cochlear damage.

The air breathing group suffered the greatest electrophysiologic threshold shift and total hair cell loss, but the differences among groups were not statistically significant. There were however trends in the histologic results which suggest that a mixture high in CO₂ may decrease the amount of postnoise exposure auditory damage in the apical part of the cochlea. The results are compared to those of other studies which report Carbogen to reduce noise-induced auditory damage.